1. Field of the Invention
The present invention relates generally to face modifying apparatus for modifying the surface of in molded products. More particularly, the present invention relates to surface modifying apparatus for modifying the surface of resin molded products containing the major component a polyolefin having relatively low face polarity, such as polypropylene.
2. Description of the Related Art
Resin molded products of polyolefins, typified by polypropyelene, are known to have relatively low surface polarity, so that it is difficult to effectively apply secondary surface treatments including coatings. Thus, when a polyolefin resin molded product is to be coated, the face of the product is first subjected to washing and modification such as roughening, using a solvent, for example, trichloroethane. Next, the thus washed and modified surface is subjected to a primer coating treatment or a plasma treatment. The thus treated resin molded product is polarized on the surface to achieve firm adhesion of the surface of the resin molded product with a facing material.
However, restrictions are increasing on washing with halogenized hydrocarbon organic solvents, including trichloroethane are and various techniques have been proposed as substitutes for such techniques of surface-modifying the polyolefin resin molded products using these organic solvents.
A new technique is disclosed, for example, in Japanese Unexamined Patent Publication No. Hei 3-103448, in which the surface of a polypropylene resin molded product is modified with an ozone gas stream. According to this technique, the polypropylene resin molded product is surface-modified by bringing it into contact with the ozone stream to oxidize on the surface and to have polar ups attached on the surface.
However, according to this technique, it is difficult to achieve uniform modification over the entire surface of the polypropylene resin molded product, particularly products having complicated shapes. Specifically, when the surface of a resin molded product is be modified uniformly, the entire surface of the resin molded product must be uniformly brought into contact with the ozone gas stream. However, it is difficult for a gas, generally having low viscosity compared with liquids, to flow along the surface of the resin molded product after the gas first contacts that surface.
Accordingly, uniform surface modification treatment cannot be achieved unless fine portions of the resin molded product are brought into direct contact with the ozone stream by moving the resin molded product or by changing angle at which the ozone stream is directed forward that surface. Thus, the number working steps is increased in order to achieve such uniform surface modification, making it difficult in to improve work efficiency.
With a view to coping with such inconvenience, the present inventors proposed a technique of oxidizing the surface of a polyolefin resin molded product by bringing it into contact with an aqueous ozone solution in Japanese Unexamined Patent Publication No. Hei 6-248103. According to this technique, the use of an organic solvent in the step prior to the surface modification step is omitted, and thus the surface of the resin molded product can be modified easily and uniformly. Therefore, when a coating is applied to the thus modified surface, the surface of the resin molded product and the coating layer are firmly adhered, and durability of the coating film is expected to improved.
However, since according to this technique the modification treatment is carried out by immersing the polyolefin resin molded product in the aqueous ozone solution at a predetermined temperature, the following inconveniences are liable to occur.
Specifically, as shown in FIG. 10, before a resin molded product 51 is immersed in the aqueous ozone solution in vessel 54, the product 51 is subjected to washing with water from jet nozzles 52 to wash off extraneous matters adhered on the product 51. However, this washing treatment is carried out while the product 51 is on a conveyor 53. Accordingly, when the product 51 moves to the immersion step, where it is immersed in the aqueous ozone solution, the thus washed product 51 must be transferred from the conveyor 53 into the immersion vessel 54 where it remains for treatment.
Meanwhile, in the washing step, the lower face of the product directly opposing conveyor 53 cannot be fully washed. Accordingly, during immersion contaminants adhered on that lower face may dissolve in the aqueous ozone solution contained in vessel 54. If such contaminants do dissolve in the aqueous ozone solution, the solution is contaminated, leading to the failure in achieving excellent surface modification.
Further, according to this prior art technique, since the resin molded product 51 is merely immersed in the aqueous ozone solution stored in vessel 54, resin molded ducts 51 cannot be successively brought into contact with the aqueous ozone solution containing unreacted ozone, requiring a relatively long time for achieving surface modification.
As a technique of canceling such inconvenience, there is contrived a technique of bringing the surface of resin molded product into contact with a flow of aqueous ozone solution. According to this technique, the surface modification treatment can be carried out continuously without interrupting a series of steps employing, for example, a conveyor. Besides, the resin molded products 51 can be constantly brought into contact with an aqueous ozone solution that contains unreacted ozone.
However, it is difficult to achieve modification uniformly over the entire surface of the resin molded product merely by bringing the resin molded product into contact with the flow of an aqueous ozone solution. More specifically, in this prior art technique, modification progresses more at those proportions of the resin molded product that are brought into frequent contact with the flow of aqueous ozone solution supplied, for example, from shower nozzles, but modification will be more difficult with those portions which are not brought into frequent contact with such flow. Accordingly, the surface of the resin molded product is nonuniformly modified depending on the degree of modification treatment achieved, and when the thus treated product is then subjected to a secondary treatment such as coating, the coating strength will likely be nonuniform.